The atomising and spray depositing of a stream of liquid metal has been known for many years, for example from British Patent Specification No: 1262471, and our own British Patent Specification Nos: 1379261 and 1472939. However, it has always been a problem to achieve precise control of the mass deposition in the metal on the deposition surface.
One proposal to improve the control of the mass distribution of the deposited layer of gas atomised of metal is set out in British Patent Specification No: 1455862 where it is proposed to oscillate the spray of atomised particles by the use of a primary set of gas jets for atomisation and two sets of secondary jets which are rapidly switched on and off to impart an oscillatory motion to the spray of atomised metal.
However, it was found that the arrangement did not give ideal control of the mass distribution of the metal deposited. Therefore, an alternative proposal for imparting a direction to a spray was suggested as disclosed in European Patent Publication No: 0127303A. That arrangement involves the switching on and off of individual gas jets which accomplish the function of both atomising and oscillating the spray. However, both these methods are very difficult to control, and in particular lack flexibility in operation.
In the first proposal the use of secondary jets can result in excess cooling of the deposited metal meaning that subsequently arriving particles do not coalesce properly with the already deposited metal. In the second method the shape and properties (eg temperature) of the spray can change as individual jets are switched on and off which makes it extremely difficult to ensure uniform deposition and solidification conditions.